The purpose of this project is to develop an accurate model of neural responses to intramodiolar and intracochlear electrical stimulation. The first part of the project will focus on intramodiolar stimulation, as such stimulation will force excitation to occur in a portion of the neuron with a regular anatomical geometry. Patterns of single-unit responses to intramodiolar stimulation will be recorded in the cat. The recorded patterns will be compared with predictions of a numerical model of cochlear neurons. The model parameters will be modified so that model predictions will comply with experimental measures of excitation, refraction, adaptation and potentiation. In addition, a stochastic component will be added to the model to account for stochastic properties of recorded unit activity (e.g., in measures of response probability versus stimulus amplitude). Once an accurate model of responses to intramodiolar stimulation has been developed, we plan to extend that model for investigation of possible effects of peripheral neuron anatomy on responses to intracochlear stimulation. Specific features to be evaluated include (1) conduction anomalies across the cell soma in the spiral ganglion; (2) site of excitation along the length of cochlear neurons; (3) influence of pathological neural anatomy on,stimulus response; (4) stochastic behavior of different nodes, e.g., differences in behavior for large versus small nodal areas; and (5) responses to patterns of electric fields predicted by a finite-element model of intracochlear electrodes. Observed effects will be used to design experiments for evaluation of model predictions. We expect that the present project will provide an accurate model of intramodiolar and intracochlear stimulation. In addition, the project will help to identify anatomical features and electrode geometries that may influence neural responses to intracochlear stimulation. Such information could be applied in the design of improved auditory prostheses.